This invention relates generally to a dispensing pump of the pressure accumulating type, and more particularly to such a pump in which its piston forms a separate part from that of the pump body which includes a closure cap for securing the pump body to a container of flowable product to be dispensed, the separate piston being of a material which is softer and more compliant than that of the pump body.
The aforementioned related application discloses a pump of the pressure-accumulating type which improves upon the dispensing pump disclosed in my U.S. Pat. No. 4,050,613 by the provision of a container vent chamber opening and closing feature. An annular lip seal on an upstanding piston engages a surrounding reciprocable plunger/accumulator and therewith defines a variable volume pump chamber, and a vent seal on the plunger skirt engages a surrounding cylindrical wall for therewith defining a container vent chamber which includes a vent opening. The piston lip seal is designed to prevent leakage of product from the pump chamber during the plunger compression stroke (except at the end of a full downstroke during pump priming), and the vent seal is designed to prevent leakage of product from the vent chamber in a raised position of the plunger and during an initial downstroke thereof.
The pump body of this pump, which includes a closure cap capable of tightly sealing the pump body over the neck of the container of flowable product to be dispensed, should be rugged and of a relatively hard material to withstand the rigors of securing the pump body on to the container. On the other hand, the piston should be of a more pliant and softer material so that its lip seal is capable of more precisely conforming to the tubular shape of the plunger/accumulator and to any irregularities in that shape to avoid leakage from the pump chamber.
Moreover, the plunger head needs to be of a rugged and relatively hard material to not only withstand repeated manipulation during the pumping operation, but to provide a reliable stop for limiting its fully raised position above pump body as a stop shoulder on its skirt engages a stop shoulder on the pump body or on the piston member in such fully raised position. And, it is desirable for the plunger/accumulator to be a softer and more pliant material so that its lip seal will conform more precisely to the cylindrical vent chamber wall on the pump body and to any irregularities in that wall so as to avoid undesirable leakage of product from the vent chamber.
In many dispensing pumps of the pressure accumulating type, the piston is formed integrally with the pump body, thereby making it difficult to fulfill the need for both a rigid pump body and a softer and more compliant pump piston.
Moreover, since the pump pistons of the pumps shown in the aforementioned related application likewise function as an inlet valve control, the types of inlet valves available are limited when the piston is made integral with the body and/or when the piston is not of a sufficiently pliant material for accurately controlling the opening and closing of the inlet.